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US Temperature Projections

Published: May 19th, 2009

This image shows projected increases in average US temperatures by 2100 compared to the late 20th century if current fossil fuel use trends continue. Different regions will warm by different amounts, as indicated by the color scale.

An advanced computer model of the global climate system, developed at the National Center for Atmospheric Research (NCAR), generated the detailed regional projections shown here. This “general circulation model” starts out with historical and projected CO2 emissions, then simulates physical processes in the atmosphere, land, ice and oceans, and how they interact.

Future emissions are obviously unknown, so in 2000, the Intergovernmental Panel on Climate Change (IPCC) defined a set of standard emissions forecasts to use in climate models. The temperature projections here are based on a scenario called A1FI, which is the most fossil-fuel intensive of these. It comes closest to actual global emissions since 2000 but real emissions have been just exceeding it in recent years.

The most recent IPCC report did not include detailed regional analysis of the A1FI scenario. Priority was given to less fossil-fuel intensive scenarios when the experiments for the last report were designed, predating the recent surge in emissions. However, the IPCC report did consider A1FI at the global level, using simple models, and estimated it would cause roughly 7°F in worldwide average warming by 2100. This would translate to about 9°F warming in the US. The NCAR model used here projected similar increases centered around 7.7°F globally and 10.1°F for the US, which climate models project will heat up faster than the globe as a whole.1

Other recent work projects even greater global increases (e.g. the MIT Joint Program on the Science and Policy of Global Change, 7.4 to 9.2°F) and, consequently, US increases.

The assistance of Gary Strand (CCR/CGD, NCAR) in providing the model results underlying this graphic is gratefully acknowledged.